The present invention relates generally to acapsBMcapsBMn electrically regenerable filter assembly. More specifically, the present invention relates to the regenerable self-cleaning filter construction that can be employed in a filter system for removing carbon, lube oil and unburned fuel particulates from the exhaust of internal combustion engines. In addition, the present invention relates to a regenerable filter construction for removing particulates from Diesel engine exhaust gases.
In the automotive industry, there has been a tremendous concern over the introduction of harmful pollutants into the air which have been generated by vehicle exhaust. Due to the negative health effects of such emissions, the Environmental Protection Agency of the United States has expressed a desire to reduce particle emissions from internal combustion engines. In the United States, the majority of particulate emissions come from Diesel engines on trucks and buses, which have not been regulated as closely as vehicles with gasoline engines.
Various attempts have been made to decrease the particulate emissions from Diesel engines. Unlike with gasoline engine vehicles, existing catalytic converters do not work well with Diesel engines since particulates typically clog these devices since the temperatures within them are too low to effectively burn carbon, lube oil and unburned fuel particles. Other efforts have been made to specifically address the Diesel particulate emissions problem. For example, fired burner systems have been employed to heat a combustion chamber, which receives Diesel exhaust for the purpose of burning the particulates within the chamber at very high temperatures. Such combustion chambers suffer from the drawbacks of high initial cost, safety, complexity, high-energy consumption and high maintenance cost.
Another prior art attempt is the employment of passive particle filters and configurations to trap the particulates associated with Diesel emissions. These passive particle filters are commonly made from ceramic, for example. These passive particulate filters are inadequate because when the filter fills up with carbon particles, the back pressure within the exhaust increases to such a level which necessitates that the filter be either regenerated in some fashion or replaced entirely. Since replacing the filter is not practical, many types of regeneration have been attempted, including the raising of the temperature of the filter above the combustion point of the carbon particulates in similar fashion to a self-cleaning oven. These prior art methods of filter regeneration include using a fired burner assembly using some type of fuel; raising the exhaust gas temperature by engine management, injecting fuel in the exhaust stream, or by electrical heating; Also by reducing the ignition temperature of carbon particles by adding heavy metal catalysts to the fuel and/or by coating filter material with suitable precious metal catalysts; The foregoing methods of filter regeneration have several disadvantages including low safety in the case of burners and fuel injection, unknown health effects in the case of heavy metal additives, and complexity in the case of using combination of these methods.
Further, there have been prior art attempts to employ electrically regenerable filter media instead of the passive filters that need to be replaced and fired burner systems which burn off the collected particulate matter. In the prior art, the filter media can be actively regenerated by heating the filter media indirectly which is typically done by a electrically resistive heater wire positioned proximal to the filter media to be regenerated; In this case, the filter media is made of non-conductive material such as ceramic or silicon carbide fibers. When current is passed through the heater wire, it heats up to raise the temperature of the filter media to, in turn, burn off the collected particulate matter to achieve regeneration. Heating the filter media indirectly results in long regeneration time, high energy consumption and incomplete regeneration.
As can be understood, multiple layers of filter media are commonly employed to improve the overall efficiency of the overall filter construction within a filter system. For example, the upstream filter can be more course while the downstream filter is more fine to improve the filtration efficiency and increase the dirt holding capacity. These layers can be provided in many different configurations in a given system. For example, the layers can be configured to be flat members that are stacked on top of one another. In this case, the exhaust flow, with particulate matter therein, is passed across the layers. Alternatively, the layers can be configured as cylindrical members that are concentrically positioned about one another. In this case, exhaust flow is typically direction through the inside of the inner cylindrical layer, through the layers and then out through the outer surface of the outer cylindrical layer.
In the prior art, the employment of multiple layers requires the use of multiple heater wires for proper operation of the filter system. Each of these heater wires must be routed proximal to their corresponding layer and also electrically interconnected to one another to one or more power sources requiring additional circuit design. The necessity for separate heater wires requires a much more complex construction than a passive filter construction which has no such heater wires. Further, this electrical interconnection of the heater wires adds complexity to the circuit design of the filter media construction and the assembly into which it is installed. Thus, in these prior art multiple layer assemblies, it is difficult to electrically isolate the layers for controlled independent heating. As a result, prior art multiple layer filter constructions are complex to design and more expensive to manufacture.
In view of the foregoing, there is a demand for a low energy regenerable Diesel exhaust filter construction that can be used in a system which can successfully remove carbon, lube oil and unburned fuel particulates from the exhaust of a Diesel engine. It is particularly desirable that the filter construction be multi-layer to improve the overall filtration efficiency of the filter construction without employing any additional energy resources of the engine. It is desirable that the multi-layered filter construction be directly heated without requiring separate resistive heater wires or separate power sources for each of the wires, i.e. the filter and heating element are one and the same. It is also desirable that a multi-layered filter construction have the capability of separately controlling of the amount of heat generated and the associated regeneration at the individual layers to better customize the operation and characteristics of the filter construction. It is also desirable that the regenerable filter system be compact and inexpensive to manufacture and use while being efficient in the field. It is desirable for a filter system to not impact the fuel economy of the engine or electrical system of the vehicle while still providing an efficient filter system. Further, it is desirable that the filter system is reliable over long periods of time without maintenance while improving the overall performance and particle holding capacity, even at low differential pressure.